The images, released by the FBI, bear out the descriptions of the two young men by those who knew them. Dzhokhar Tsarnaev, who has been described as "very relaxed", appears to be grinning, his dark curls covered by a white baseball cap. His older brother, Tamerlan, shields his eyes with sunglasses, his mouth slightly open as he stares ahead.

The two ethnic Chechens, who were identified on Friday as the chief suspects in the bombings, followed a convoluted path to the United States, like so many from the troubled Russian republic. Although it appears that they never lived in Chechnya, which has spent much of the past two decades racked by war, they maintained close ties to its culture.

There are conflicting reports in regards to the birth places of the Tsarnaev brothers. Local police, cited in Kyrgyz media, suggest that both were born in Kyrgyzstan. But family members in the US said the younger brother, Dzhokhar, was born in Dagestan. The brothers are thought to have spent some of their youth in the city of Tomok, the centre of Kyrgyzstan's Chechen community, which developed after Josef Stalin expelled hundreds of thousands of Chechens around central Asia during the second world war.

Little is known of the brothers' time in Kyrgyzstan. Tamerlan Tsarnaev, 26, who was shot dead by Boston police in the early hours of Friday morning, was born in 1986. His younger brother, 19 and on the run, was born in July 1993. The following year, Chechnya would break out into the first of two wars, as it fought to secede from Russia in the wake of the Soviet Union's collapse. Moscow responded with unbridled brutality, being accused of widespread human rights abuses against the civilian population. The rebels in the mainly Muslim republic grew ever more Islamist.

The Tsarnaev family moved to Dagestan, a Muslim republic neighbouring Chechnya, sometime between 1999 and 2001. According to his page on the Russian social network VKontakte, the younger Tsarnaev attended School Number One in Makhachkala, Dagestan's capital. Irina Bandurina, an administrator at the school, said Tsarnaev studied there in 2001, after moving from Kyrgyzstan, and left for the United States in 2002.

Tamerlan Tsarnaev, left, and Dzhokhar Tsarnaev. Photograph: AP

The family appears to have settled in Cambridge, Massachusetts. But according to US law enforcement officials cited by the Wall Street Journal, the two brothers arrived separately: one with his parents in 2002, the other in 2004. The officials said that one or both of the brothers had returned to the Caucasus for some time after emigrating to the US.

Tamerlan is thought to have spent around six months of last year out of the US, during which time he saw his father in Dagestan. Anzor Tsarnaev told the New York Times that during the visit he and his son "went to Chechnya to visit relatives".

Authorities in Chechnya, in the midst of a massive campaign to show that life in the republic has normalised despite a continuing low-level insurgency, harshly denied any links to the brothers. "Any attempt to make a link between Chechnya and the Tsarnaevs, if found guilty, is in vain," the republic's leader, Ramzan Kadyrov, wrote on Instagram on Friday. "They grew up in the US, their views and beliefs were formed there. The roots of evil must be searched for in America."

Yet the brothers left internet evidence that showed their deep ties to the republic. The last entry on Dzhokhar Tsarnaev's page on VKontakte, posted on 19 March, shows a video of his brother humorously imitating various accents from the region, in fluent Russian. It shows that among the three groups to which he belongs are "Chechen's" and "Chechnya: Everything about the Chechen Republic".

Tamerlan Tsarnaev's links run even deeper. A YouTube account that appears to have been run by the elder Tsarnaev includes a playlist devoted to Timur Mutsuraev, a Chechen singer now in exile who sang of the republic's battle for freedom from Russia. His account also includes a playlist devoted to "terrorism", including one video in English entitled "The Emergence of Prophecy: The Black Flags from Khorasan". He also maintained a playlist devoted to Islam.

Chechnya's separatist cause struck Tamerlan Tsarnaev deeply, according to a report by photographer Johannes Hirn, who profiled the young Chechen when he was training for a boxing match in 2010. One caption in the report reads: "Unless his native Chechnya becomes independent, Tamerlan says he would rather compete for the United States than for Russia." The elder Tsarnaev fought for a while as a competitive boxer, taking time off from his studies at Bunker Hill community college in Charlestown, Massachusetts.

The report also shows him to have been very religious, and poorly integrated in the US. According to Hirn's report, the Chechen once said: "I don't have a single American friend, I don't understand them." In 2009, Tsarnaev was reportedly arrested for assaulting his girlfriend. His aunt, who lives in Canada, told reporters on Friday that the elder brother had married and that the couple had a three-year-old daughter living in the US.

• This article was amended on 23 April 2013 to correct the spelling of Charlestown, from Charleston.